From EP 0 776 275 B1 an axle suspension for rigid axles of vehicles is known, wherein the vehicle axle is connected to the vehicle body by means of longitudinal control arms and a four-point link. Articulated joints for fixation to the vehicle body and articulated joints for fixation to the vehicle axle are arranged at the arm ends of the four-point link configured as an X-shaped cross. The cross-sectional profile of the arms may be double T-shaped or comprise a hollow profile.
DE 100 50 772 A1 discloses an axle suspension for rigid axles of vehicles, comprising two trailing links connecting the rigid axle to the vehicle body and a four-point linkage, which is both connected in an articulated manner to the rigid axle and connected in an articulated manner to the vehicle body. The four-point link comprises a hollow component extending parallel to the longitudinal direction of the vehicle, at the end of which two articulated arms are provided that are arranged symmetrically to the longitudinal axis of the component and fastened thereon.
DE 10 2004 014 610 A1 describes an X-shaped four-point suspension arm for the suspension of a rigid axle of a commercial vehicle, comprising a central, hollow housing region and four link arms integrally molded on the housing region, at the outer ends of which bearing lugs provided with ball joints and/or elastomer joints are integrally molded. The hollow housing of the four-point link is open on both sides and has a tubular shape, and is waisted on all four sides. The link arms further have a U-shaped or C-shaped cross-section and merge smoothly into the central, tubular housing region. The hollow housing may be configured as a sheet metal part or cast iron part, wherein the four-point link is made, for example, of bainitic cast iron.
In practice, for manufacturing reasons, cost reasons, strength reasons and weight reasons, two shapes have proven especially efficient. This is the X-shape on the one hand, which has been manufactured primarily by forging. In this case, for manufacturing reasons, a solid rectangular cross-section is achieved as the arm cross-section, which may be adjusted in a relatively simple manner to the required characteristic and strength properties. The disadvantage for more economical production, for example by casting, of a hollow geometry according to EP 0 776 275 B1 is that they are completely closed. As a result, process-reliable support of the core forming the hollow space is not possible, or only with a lot of restrictions. This may produce irregular wall thicknesses, and thus negative strength properties, from core floating during casting. The disadvantages of the existing X-geometry produced by forging is the rectangular cross-section thereof predetermined by the production method, resulting in heavy components and consequently high costs. For a torsionally flexible forged four-point link, the arms are normally configured very flat. This may result in the problem that the housing heads are not completely filled during forging. An X-geometry with a double T-shaped arm cross-section requires several cores for casting, which increases the cost of the component. In addition, the double-T profile is disadvantageous for lateral loads.
On the other hand, the casting design open on both sides according to DE 10 2004 014 610 A1 has proven effective. This shape is characterized by cost-effective and lightweight forging as well as by the hollow construction, and thus offers several advantages compared to the forged four-point link. The design, however, reaches its limit with flexible torsional characteristics. In order to configure a more flexible characteristic, for example, either the wall thickness or the core height is reduced. Both measures, however, have manufacturing barriers. The wall thickness should have a minimum dimension so that the component can be cast, and the core should have a minimum height so that it does not break due to the buoyancy of the liquid cast iron. Therefore, this shape is less suitable for the application of a torsionally flexible characteristic. A reduction in the torsional characteristics by means of a narrower component is only possible to a very limited extent for reasons of operational stability.
In the four-point link according to DE 100 50 772 A1, which substantially comprises a tube with small arms for connection, the torsional characteristic is determined almost exclusively by the tube. The disadvantage of this design is the manufacturing technology. The geometry of the four-point link can normally not be forged because of to the tubular profile. In addition, the four-point link is suitable for production by casting only to a limited extent, because the inside diameter should not be below a minimum dimension due to the required stability of the long core. As the arms are configured as a rectangular profile, there is the risk of blowhole formation if they are not configured very thin. In addition, this geometry is not designed appropriate to the load. With torsionally flexible characteristics, the tubular profile in the center has to be very thin, or have a small cross-section, and thus offers little resistance to lateral loads. The arms configured as a thin rectangular profile also offer little resistance to lateral loads. In addition, the link exhibits changes in stiffness at the transition of the arms to the tube, which is disadvantageous for operational stability.